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    <title>ShellCheck: SC2100 – Use `$((..))` for arithmetics, e.g. `i=$((i + 2))`</title>
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    <h1>SC2100 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2100">See this page on GitHub</a>
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    <h2 id="use--for-arithmetics-eg-ii--2">Use <code>$((..))</code> for
arithmetics, e.g. <code>i=$((i + 2))</code></h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2100.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="va">i</span><span class="op">=</span>3</span>
<span id="cb1-2"><a href="SC2100.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="va">i</span><span class="op">=</span>i+2</span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2100.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="va">i</span><span class="op">=</span>3</span>
<span id="cb2-2"><a href="SC2100.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="va">i</span><span class="op">=</span><span class="va">$((i</span> <span class="op">+</span> <span class="dv">2</span><span class="va">))</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>Unlike most languages, variable assignments (almost) always assigns
strings and not expressions. In the example code, <code>i</code> will
become the string <code>i+2</code> instead of the intended
<code>5</code>.</p>
<p>To instead evaluate a mathematical expressions, use
<code>$((..))</code> as in the correct code.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>If you wanted to assign a literal string, quote it:</p>
<pre><code>description=&quot;friendly-looking&quot;</code></pre>
<p>ShellCheck (as of v0.5) doesn't recognize Bash/Ksh numeric variables
created with <code>declare -i</code> where this syntax is valid. Using
<code>$((..))</code> still works, but you can also <a
href="ignore.html">ignore</a> this warning.</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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